Periodically corrugated surfaces (gratings) are widely used in many different optoelectronic devices. For example, a surface grating structure can be used to provide a feedback path for distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers. Externally modulated laser (EML) structures also employ a grating structure. Such state-of-the-art devices are currently being deployed in dense wavelength division multiplex (DWDM) systems that require channel spacing of approximately 0.8 nm. This extremely narrow spacing translates into a 7 .ANG. period difference between transmission channels.
During the manufacturing process, it is important to be able to measure the grating periodicity to ensure that the proper channel spacing is obtained. Current measurement arrangements rely on diffraction techniques and require operator judgement for both set-up and calibration of each measurement. In many systems, Ar ion gas lasers are used to generate the needed UV laser beam. These lasers are large and expensive to maintain.
Thus, a need remains in the art for a grating measurement arrangement that is suitable for the manufacturing environment and is capable of providing accurate measurements of sub-Angstrom grating periods.